1. Field of the Invention
This invention relates to a lens turret which holds a plurality of lenses and a support therefore for holding the lenses above an object to be viewed, and more particularly, to a lens turret support arrangement which includes provision for rapidly rotating the turret to move a viewing lens out of the object viewing location and to move an adjacent lens into said viewing location, for precisely positioning the lens in the viewing location and for raising or lowering the turret in precise increments over a short distance for focusing the lens on the object.
2. Description of the Prior Art
Lens turret and supports therefore are well known and techniques for rotating the turret to bring a lens into viewing position most often use detent notches and a detent ball that rides on the surface of the turret as it is rotated between adjacent detent notches. This causes wear of the turret periphery as well as the notches and also impedes the speed of rotation as the turret rotates. The wear causes errors in positioning, and may release metal particles as contamination which cannot be tolerated where highly accurate positioning is necessary such as is required for the automatic inspection of nonpatterned or patterned wafers. Also, such rotational drives are not adequately isolated from the turret support. The lens is normally focused manually by means of a control knob associated with a gear drive arrangement. Even where some non-manual drive is provided, a gear arrangement is commonly used. This introduces friction and backlash that is not acceptable to precise automatic focusing of a lens on an object.